Obesity increases both the incidence and mortality of numerous types of cancer. Children and adults who are obese at the time of diagnosis of high-risk acute lymphoblastic leukemia (ALL) have a 50% increased risk of relapse compared to their lean counterparts. Using mouse and tissue culture models, we showed that obesity directly impacts the progression and treatment outcome of ALL. We discovered that adipocytes protect ALL cells from a number of chemotherapies, including the anthracycline daunorubicin (DNR). We have found that fat cells break down DNR to an inactive form, which depletes local levels and protects nearby ALL cells from this chemotherapy. In the present grant, we will further elucidate this mechanism, using a combination of cell culture, mouse experiments, and clinical studies. We will first investigate which enzymes in adipocytes contribute to their ability to breakdown anthracyclines like DNR, and explore strategies to block these enzymes. We will use mouse models to determine how adipocytes in vivo alter systemic DNR availability, as well as that in the bone marrow and other ALL microenvironments. We will also explore how clinical variables such as age and gender alter these effects. Finally, we will perform a limited sampling PK study in lean and obese children, to estimate DNR and DNR-ol plasma and intracellular exposure during ALL therapy. These studies will increase our understanding of how the leukemia microenvironment can contribute to treatment failure, particularly in the obese state. Findings could lead to improved strategies for anthracycline dosing and monitoring in children and adults. These results, along with our previous studies on how adipocytes affect vincristine and L-asparaginase PK and PD, will lay the groundwork for a personalized dosing study of Induction chemotherapies in children with ALL.